var BASE64_MAPPING = [
  'A','B','C','D','E','F','G','H',
  'I','J','K','L','M','N','O','P',
  'Q','R','S','T','U','V','W','X',
  'Y','Z','a','b','c','d','e','f',
  'g','h','i','j','k','l','m','n',
  'o','p','q','r','s','t','u','v',
  'w','x','y','z','0','1','2','3',
  '4','5','6','7','8','9','+','/'
];

/**
 *ascii convert to binary
 */
var _toBinary = function(ascii){
  var binary = new Array();
  while(ascii > 0){
    var b = ascii%2;
    ascii = Math.floor(ascii/2);
    binary.push(b);
  }
  /*
  var len = binary.length;
  if(6-len > 0){
      for(var i = 6-len ; i > 0 ; --i){
          binary.push(0);
      }
  }*/
  binary.reverse();
  return binary;
};

/**
 *binary convert to decimal
 */
var _toDecimal  = function(binary){
  var dec = 0;
  var p = 0;
  for(var i = binary.length-1 ; i >= 0 ; --i){
    var b = binary[i];
    if(b == 1){
      dec += Math.pow(2 , p);
    }
    ++p;
  }
  return dec;
};

/**
 *unicode convert to utf-8
 */
var _toUTF8Binary = function(c , binaryArray){
  var mustLen = (8-(c+1)) + ((c-1)*6);
  var fatLen = binaryArray.length;
  var diff = mustLen - fatLen;
  while(--diff >= 0){
    binaryArray.unshift(0);
  }
  var binary = [];
  var _c = c;
  while(--_c >= 0){
    binary.push(1);
  }
  binary.push(0);
  var i = 0 , len = 8 - (c+1);
  for(; i < len ; ++i){
    binary.push(binaryArray[i]);
  }

  for(var j = 0 ; j < c-1 ; ++j){
    binary.push(1);
    binary.push(0);
    var sum = 6;
    while(--sum >= 0){
      binary.push(binaryArray[i++]);
    }
  }
  return binary;
};

export var BASE64 = {
  /**
   *BASE64 Encode
   */
  encoder:function(str){
    var base64_Index = [];
    var binaryArray = [];
    for(var i = 0 , len = str.length ; i < len ; ++i){
      var unicode = str.charCodeAt(i);
      var _tmpBinary = _toBinary(unicode);
      if(unicode < 0x80){
        var _tmpdiff = 8 - _tmpBinary.length;
        while(--_tmpdiff >= 0){
          _tmpBinary.unshift(0);
        }
        binaryArray = binaryArray.concat(_tmpBinary);
      }else if(unicode >= 0x80 && unicode <= 0x7FF){
        binaryArray = binaryArray.concat(_toUTF8Binary(2 , _tmpBinary));
      }else if(unicode >= 0x800 && unicode <= 0xFFFF){//UTF-8 3byte
        binaryArray = binaryArray.concat(_toUTF8Binary(3 , _tmpBinary));
      }else if(unicode >= 0x10000 && unicode <= 0x1FFFFF){//UTF-8 4byte
        binaryArray = binaryArray.concat(_toUTF8Binary(4 , _tmpBinary));
      }else if(unicode >= 0x200000 && unicode <= 0x3FFFFFF){//UTF-8 5byte
        binaryArray = binaryArray.concat(_toUTF8Binary(5 , _tmpBinary));
      }else if(unicode >= 4000000 && unicode <= 0x7FFFFFFF){//UTF-8 6byte
        binaryArray = binaryArray.concat(_toUTF8Binary(6 , _tmpBinary));
      }
    }

    var extra_Zero_Count = 0;
    for(var i = 0 , len = binaryArray.length ; i < len ; i+=6){
      var diff = (i+6)-len;
      if(diff == 2){
        extra_Zero_Count = 2;
      }else if(diff == 4){
        extra_Zero_Count = 4;
      }
      //if(extra_Zero_Count > 0){
      //  len += extra_Zero_Count+1;
      //}
      var _tmpExtra_Zero_Count = extra_Zero_Count;
      while(--_tmpExtra_Zero_Count >= 0){
        binaryArray.push(0);
      }
      base64_Index.push(_toDecimal(binaryArray.slice(i , i+6)));
    }

    var base64 = '';
    for(var i = 0 , len = base64_Index.length ; i < len ; ++i){
      base64 += BASE64_MAPPING[base64_Index[i]];
    }

    for(var i = 0 , len = extra_Zero_Count/2 ; i < len ; ++i){
      base64 += '=';
    }
    return base64;
  },
  /**
   *BASE64  Decode for UTF-8
   */
  decoder : function(_base64Str){
    var _len = _base64Str.length;
    var extra_Zero_Count = 0;
    /**
     *计算在进行BASE64编码的时候，补了几个0
     */
    if(_base64Str.charAt(_len-1) == '='){
      //alert(_base64Str.charAt(_len-1));
      //alert(_base64Str.charAt(_len-2));
      if(_base64Str.charAt(_len-2) == '='){//两个等号说明补了4个0
        extra_Zero_Count = 4;
        _base64Str = _base64Str.substring(0 , _len-2);
      }else{//一个等号说明补了2个0
        extra_Zero_Count = 2;
        _base64Str = _base64Str.substring(0 , _len - 1);
      }
    }

    var binaryArray = [];
    for(var i = 0 , len = _base64Str.length; i < len ; ++i){
      var c = _base64Str.charAt(i);
      for(var j = 0 , size = BASE64_MAPPING.length ; j < size ; ++j){
        if(c == BASE64_MAPPING[j]){
          var _tmp = _toBinary(j);
          /*不足6位的补0*/
          var _tmpLen = _tmp.length;
          if(6-_tmpLen > 0){
            for(var k = 6-_tmpLen ; k > 0 ; --k){
              _tmp.unshift(0);
            }
          }
          binaryArray = binaryArray.concat(_tmp);
          break;
        }
      }
    }

    if(extra_Zero_Count > 0){
      binaryArray = binaryArray.slice(0 , binaryArray.length - extra_Zero_Count);
    }

    var unicode = [];
    var unicodeBinary = [];
    for(var i = 0 , len = binaryArray.length ; i < len ; ){
      if(binaryArray[i] == 0){
        unicode=unicode.concat(_toDecimal(binaryArray.slice(i,i+8)));
        i += 8;
      }else{
        var sum = 0;
        while(i < len){
          if(binaryArray[i] == 1){
            ++sum;
          }else{
            break;
          }
          ++i;
        }
        unicodeBinary = unicodeBinary.concat(binaryArray.slice(i+1 , i+8-sum));
        i += 8 - sum;
        while(sum > 1){
          unicodeBinary = unicodeBinary.concat(binaryArray.slice(i+2 , i+8));
          i += 8;
          --sum;
        }
        unicode = unicode.concat(_toDecimal(unicodeBinary));
        unicodeBinary = [];
      }
    }
    //---------直接转换为结果
    var strResult = '';
    for(var i = 0 , len =  unicode.length ; i < len ;++i){
      strResult += String.fromCharCode(unicode[i]);
    }
    return strResult;
  }
};
